The blades and disks of the rotor of rotating machines, in the event of rupture, may cause very serious or even catastrophic secondary effects, in particular when the engine involved is propelling an aircraft.
In order to limit the consequences of such incidents, the housings of compressors and turbines have been surrounded by thick armor plating made of steel. The principal disadvantage of this solution is the added weight which penalizes the performance of the engine, and if the fragments are retained inside the housing and do not damage the other elements of the engine, this retention itself is often the cause of chain rupturing of the blades, which strike the fragments blocked within the housing. This results in an explosion of the rotor or the tearing of the engine from its support.
Designers have been searching for solutions of this problem. Thus, French Pat. No. 2,018,042 describes retaining means consisting of the housing and metal wound around its external surface. The direction of the winding of the bands is opposed to the normal direction of rotation and has the effect that when the detached fragment of the rotor strikes the bands and drags them along, the windings are tightened, which creates heavy friction to absorb the kinetic energy. The windings are limited by the elasticity of the material constituting the bands because of the fastening of their ends to the housing and the stationary mounting structure of the engine. The kinetic energy of the fragment contacting the bands has been partially absorbed by the work required to perforate or to deform the housing.
French Pat. No. 2,375,443 describes a casing ring comprising a layer of a lightweight material, specifically such as a honeycomb fastened to the retaining ring and having high mechanical strength. This ring is itself supported by wings capable of being crushed during the deformation of the retaining ring. The casing ring is maintained in a support by means of pins or by friction so that it may rotate under the impact of the fragment detached from the rotor and absorb the kinetic energy even when the retaining ring is deformed.
Finally, French Pat. No. 1,435,869 proposes a retaining ring made of an elastic and flexible material mounted in a manner so that it is free to move radially toward the outside in contact with the envelope by means of the deformation or rupture of the supporting tenons.
A retaining casing must combine three conditions which are only partially satisfied by the preceding designs, i.e. the rapid removal of the fragments from the enclosure of the rotor, the absorption of energy, so that if the fragments should break through the casing, their residual energy would be insufficient to cause damage, and finally it should be light enough so that it will not absorb an excessive fraction of the pay-load of the aircraft.